Pump



Sept. 21, 1965 p, B, zr-:IGLER ETAL 3,207,077

PUMP

Original Filed Sept. 19. 1958 3 Sheets-Sheet l [NI/EMDRS A T TORNE Y Sept 21, 1965 P. B. zElGLx-:R ETAL 3,207,077

PUMP

Original Filed Sept. 19, 1958 3 Sheets-Sheet 2 24 Tmp/wn Sept. 21, 1965 P. B. zElGLER ETAL PUMP 3 Sheets-Sheet 3 Original Filed Sept. 19, 1958 ATTORNEY Unted States Patent O 3,207,077 PUMP Philip E. Zeigler, Saginaw, William B. Thompson, Frankenmuth, and Robert P. Rohde, Saginaw, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Continuation of application Ser. No. 762,162, Sept. 19, 1958. This application May 27, 1963, Ser. No. 283,219 11 Claims. (Cl. 10S-42) This application is a continuation of the applicants application Serial No. 762,162, filed September 19, 1958, now abandoned.

This invention relates to fluid pumps and in its most specific aspect has relation to constant or lixed displacement vane pumps which in use are operated at varying speeds. The vane pump widely employed in power steering apparatus is exemplary of pumps of this category, and the invention will be particularly described with reference thereto.

Such pump is normally driven either directly or indirectly by the lcrankshaft of the vehicle engine. Thus, the speed of operation of the pump and, hence, the rate of flow of the discharge fluid -varies as the speed of the engine. This condition is manifestly undesirable, considering that the steering resistance is lightest at the higher speeds when the pump output is greatest. While an obvious solution t-o the problem would be the substitution of a variable displacement pump, automatically controlled by means responsive to engine speed, this is not feasible from a cost standpoint.

The excessive output of the conventi-onal pump at higher speeds causes a heat build-up in the power steering system and increases leakage diflicult-ies. The heat problem has become especially acute of late because of the crowded condition of the engine compartment, which makes ventilation of accessory devices therein contained diflicult.

Another problem owing to the high-speed operation of the pump is cavitation, i.e., the development of voids in the working fluid. rI'his causes premature Wearing of the pump parts and creates noises impossible to mask completely. Although vari-ous proposals have been made with reference to the cavitation problem, such proposals demand the use of auxiliary valving or changes in manufacturing procedures, introducing excessive costs.

As above suggested, the present invention aims to reduce the output of the pump at the higher speeds and to prevent the cavitation normally occurring at such speeds without complicating the manufacture of the pump or substantially increasing its cost.

Another important object is to provide a pump having improved efficiency.

Still another object is to simplify the construction of the pump, yet with the attainment of features not possessed by the conventional pump.

`Now to identify the accompanying drawings illustrating the invention in a preferred embodiment:

FIGURE 1 is an end elevation;

FIGURE 2 is a sectional view on the line 2-2 in FIG- URE 1;

FIGURE 3 is a section on the line 3--3 in FIGURE l;

FIGURE 4 illustrates the relative disposition of certain of the pump parts;

FIGURE 5 is a generally diagrammatic representation of the flow control and anti-cavitation system and shows a slight modification of the FIGURE 2 valve structure; and

`FIGURE 6 is a graph reflective of the operation of the pump.

Referring first to FIGURES 1-3, the numeral 10 denotes a reservoir desirably formed of sheet metal and ICC encircling lthe pump proper. The reservoir will be seen as comprising a filler tube 12 having a cap 14.

A seal 16 accommodated in an annular recess in the pump casing 18, which carries a mounting piece 19, prevents leakage around the rim portion 20 of the reservoir.

Casing 18 is of one-piece construction, with inner and outer recesses 22 and 24, respectively. A cover piece 26 is encircled by a seal 28 and shoulders against a snap ring 30, both the seal and ring finding accommodation in annular recesses formed in casing 18. It is important to note that due t-o the rounded contour of cover 26 and the fact that the ring 30 is circular in section, the forces subsequently to be mentioned which tend to displace the cover 26 outwardly or rightwardly (FIGURE 2) do not tend to shear the ring, as would be the case if it were of rectangular section. Rather, such forces tend merely to more securely seat the ring in its groove. The ring is easily removed when necessary through the use of a punch inserted through the hole 31.

Extending through a journal boss 32 integral with casing 18 is a drive shaft 34 splined at its inner end for operable connection to a rotor 36. Outward of the rotor, the shaft, which has an integral iiange 34a taking thrust loads, is surrounded by a bushing 38 and a seal 40.

Rotor 36 carries a plurality of vanes 42 (note FIG- URE 4) which in operation of the pump are caused to reciprocate radially in slots 42a by a cam ring 44 within which the rotor is confined.

A pressure plate 48 at the right side of the rotor (FIGURE 2) and abutting the cam ring 44 forms a discharge chamber 50 with the cover 26. The inner face of this plate -is relieved at 48a. At the opposite or left side of the rotor and abutting the corresponding side of the cam ring 44 is a thrust plate 52 having a recessed portion 52a. As shown, this plate encircles the drive shaft 34 and bears against the wall 54 of the recess 22.

Cam ring 44 is supported within the casing 18 by pins 56 (FIGURE 3). Such pins extend through the pressure plate 48 and the thrust plate 52, as well as the cam ring, and are received within blind bores formed in the flange portion 18a of the casing 18. Outward of the pressure plate 48 the pins serve as guides for springs 58 which react against the inside of cover 26.

A feature of the arrangement involving the dowel pins 56 resides in a sleeve 37 preferably press fitted into the rotor 36 and having a close bearing fit with relation to the thrust plate 52. Such sleeve allows the rotor to partake of the alignment provided by the dowel pins and corrects for misalignments of the shaft 34.

Bolts 60, seen in FIGURE 3, secure the reservoir 10 to casing 18.

As illustrated by FIGURES 2 and 5, casing 18 outward of its center line is bored and counterbored to provide a cavity 85 for the reception of a flow control valve 64. Such valve is biased rightwardly by a spring 66, the limit of the rightward movement being set by a plug member 68 which is provided with a seal 70 and shoulders against a snap ring 72.

Chamber 50, previously mentioned as formed by pressure plate 48 and cover 26, receives the pump discharge. Such chamber opens to a short passage 76, in turn opening to a relatively long passage 78 of lesser diameter, these passages providing the connected discharge passage for conveying the pumpdischarge fr-om chamber 50. Extending from passage 78 is a branch discharge passage 80 of much smaller diameter than passage 78. Passage 80, which is actually an orifice determinative of the flow rate of the pump, communicates with the pumps outlet, or exhaust port and the fixture 81 seen in FIGURE 3.

As shown by FIGURES 2 and 5, passage 78 opens to the previously mentioned cavity housing valve 64. Also opening to such cavity is a passage 82 extending downenzow wardly from an annular chamber 84 which surrounds thrust plate 52, cam ring 44 and the relieved portion 48a of pressure plate 4S.

A passage 86, connecting with passage 82, is at all times open to the chamber a of the reservoir 10 and constitutes the inlet or intake port of the pump. Fluid returned to the reservoir from the system served thereby enters the reservoir via .a tube 89 seen in FIGURE 3. A conduit 83 opening to the cavity 85 leftward (FIG. 2) of the valve 64 connects with the orifice passage 80 as shown in FIGURE 5.

Going now to FIGUR-E 4, it will be observed that the relieved portion 48a of the pressure plate 48 is of symmetrical free-form outline `and that the plate is provided with `a pair of diametrically opposed openings 90. It is through these openings that the pump discharge passes into the `chamber 50. Portions 90a of openings 90 accommodate the previously mentioned pins 56 affording support to the cam ring 44.

Raidially inward of openings 90 are a pair of arcuate openings 92 and a pair of arcuate recesses 94 within 'which are holes 96. The purpose of openings-92 is to Iallow for the passage of fluid at discharge pressure from chamber 50 to cavities 98 (located at the innermost reaches of slots 42a) as the vanes 42 move radially outwardly. This assures proper engagement of the outer edges of the vanes with the inner contour of the cam ring 44.

Holes 96 are so placed with reference to the inner contour of cam ring 44 that they meter the ow of fluid from cavities 98 to chamber 50 as the vanes move radially inwardly. In this way, such movement of the vanes is cushioned and the life thereof extended.

The re-entrant portions 100v at the periphery of the relief 48a (plate 48) extend inwardly of the adjacent inner edge of the cam ring to provide intake ports 100a open to intake chamber 84.

From FIGURE 4,v it will be observed that thrust plate 52 is supplied with holes 102 allowing for the passage therethrough of the pins 56. Inward of such holes are recesses 104 conforming in outline with the effective portions of openings 90 in pressure plate 48. These recesses 104 are in circumferential alignment with the openings 90 and communicate therewith through the intervane chambers 91 and holes 93 in cam ring 44. Similarly, arcuate recesses 106 are in circumferential alignment with arcuate openings 92 and arcuate recesses 108 are in circumferential alignment with arcuate recesses 94.

As should be readily apparent, the periphery of thrust plate 52 matches that of the relieved portion of 48a of plate 48. Thus, since recesses 104 circumferentially register with openings 90 as described, it follows that the reentrant portions 110 circumferentially register with the re-entrant portions 100. The re-entrant portions 110, like portions 100, extend inwardly of the inner contour of cam ring 44. Accordingly, a second pair of intake ports 110a leftward (FIGURE 4) of such ring is provided.

To describe now the general operation of the pump and referring particularly to FIGURES 2 and 4, with the rotor 36 turning clockwise, fluid is drawn into the intervane chambers 81 from intake chamber 84 via ports 100a and l10n and is discharged into the discharge chamber 50 via ports 90. As the vanes move radially outwardly, discharge fluid entering the cavities 98 through openings 92 operates, as previously explained, to insure engagement of the outer ends of the vanes With the cam ring. The filling of the intervane chambers during the suction stages is made fast and complete by reason of the head of fluid in chamber 84 with which ports 100a and 110a communicate at all times.

As should be evident from FIGURE 4, the diametrically opposed relation of the suction and pressure chambers as set by the cam ring maintains the rotor 36 in radial balance. Less evident, perhaps, is the fact that the rotor is in substantial axial balance, this being the purpose of the several recesses or pockets in thrust plate 52. It is to be noted that discharge fluid entering recesses 104 passes to chamber 50 via holes 93 in cam ring 44 and ports 90 in the pressure plate.

An important feature of the construction of the thrust plate 52 goes to the recess 52a which permits of slight deflection of the plate from the force of the fluid pressure to which it is subject. This slight deflection operates to promote egress to the intake chamber 84 or the pressure chamber 50 of any foreign matter which might otherwise tend to accumulate in the recesses in the plate.

The discharge fluid, as aforenoted, leaves the pump via the passage or orifice branching from passage 78. AS- suming the pump is being used for power steering and is operating at minimum speed, i.e., assuming that the engine of the vehicle carrying the pump is idling, all of the discharge fluid normally passes through the orifice 80 and out the conduit 81 to the system, valve 64 under the indicated condition being in its closed position shown. The ow rate set by the orice 80 is, of course, a function of the diameter and length thereof. In most installations these factors are calculated to give a flow rate of from 2-3 gallons of fluid per minute, such flow rate having been found suicient to provide adequate assist with the engine idling and with the steering resistance maximum, as obtains during parking.

Let it be assumed now that the vehicle carrying the pump is traveling at highway speed. Since the pump rotor is turning at corresponding speed a pressure build-up naturally occurs in the chamber 85 because of the restriction 80. As a consequence, valve 64 is displaced leftwardly (FIG. 2 and FIG. 5) against the resistance of the spring 66 and the fluid at system pressure contained within the -spring chamber, so that the passages 78 and 82 become interconnected. Spring 66, of course, is carefully selected or gaged to yield under the indicated conditions. A relief valve, not shown, responsive to the pressure in the spring chamber and opening to intake chamber 84 when such pressure reaches a predetermind Value is normally included in the system.

As the bypass oil courses passage 82 it attains substantial velocity. Under Bernoullis principle, the kinetic energy thus developed is translated in substantial part into static pressure in the chamber 84. Since the magnitude of the statis pressure is a function of the velocity in passage 82 and since such velocity is in turn a function of the pump speed, cavitation with its undesirable manifestations is effectively prevented.

Heretofore, with the pump bypassing as described, the discharge to the system rose abruptly at a pump speed of from 350D-400() r.p.m.-note pump B in FIGURE 6, wherein pump speed is plotted as abscissae and flow rate as ordinates. Such condition, as noted in the forepart hereof, caused excessive heating of the Huid and the p-arts in contact therewith. Also, because of the increased flow rate through the system, leakage problems were prone to occur.

According to the invention, a flow rate is attained as illustrated by pump A in FIGURE 6. Thus, the flow rate is actually caused to fall off instead of increase at the higher pump speeds. Consequently, there is no heat build-up in the system such as previously experienced. This desideratum is achieved by careful control of the diameters of passages 76 and 78 relative to passage or orifice 80. Passage 78 being of lesser diameter than passage 76, fiuid flow therethrough is commensurately more rapid. At a pump speed reflected by the graph of FIG- URE 6, the fluid flowing through passage 78 begins to have a venturi-like effect with respect to the opening of the orifice 80 with the result that since the static pressure decreases at this point at the same rate as velocity pressure increases according to Bernoullis principle less Huid is permitted to pass said orifice because of the resulting decrease in static pressure drop across this orice than 5. is the case with the pump idling or operating at speeds reflective of parking conditions or low speed travel.

We claim:

1. In a constant displacement pump operated at varying speeds, said pump comprising an intake chamber, a discharge chamber and intake and exhaust ports, the combination of means providing a discharge passage having a restricted position connected to said discharge chamber, a branch discharge passage of relatively small diameter extending from said restricted portion and opening to said exhaust port, means providing a bypass passage interconnecting said discharge passage and said intake chamber, said bypass passage including a restricted portion connecting said intake port to said intake chamber, and a valve in said bypass passage upstream of said second-mentioned restricted portion and downstream of said first-mentioned restricted portion responsive to the pressure in said discharge passage, said valve being displaced to place said discharge passage in communication with said bypass passage When such pressure reaches a predetermined value determined by the diameter of said branch discharge passage, said pump being further characterized in operation in that flow of fluid in said bypass passage through said second mentioned restricted portion past said intake port has a supercharging action with respect to said intake chamber and in that with said Valve displaced and with the pump operating at a predetermined speed higher than its minimum speed the velocity of the fluid flowing in said first-mentioned restricted portion past said branch discharge passage operates to limit the flow rate from said exhaust port.

2. In a constant displacement pump operated at vary- Y ing speeds, said pump comprising an intake chamber, a

discharge chamber and intake and exhaust ports, the combination of means providing adischarge passage extending from said discharge chamber including -a first section of relatively large diameter and ,a second section of relatively small diameter downstream of said first section having a branch discharge passage lof still smaller diameter communicating with said exhaust port, means providing a bypass passage interconnecting said discharge passage and said intake chamber, said bypass passage including a first ysection of relatively large diameter and a second section of relatively small diameter downstream of said last-mentioned first section communicating said intake port with said intake chamber, and a valve in said bypass passage upstream of said last-mentioned first section responsive to the pressure in :said discharge passage as reflected in said last-mentioned first section, said valve being displaced to place said discharge passage in communication with said bypass passage when such pressure reaches a predetermined value determined by the diameter of -said branch discharge passage, said pump being further characterized in operation in that flow of fluid in said lastmentioned second section past said intake port has a supercharging action with respect to said intake chamber and in that with said valve displaced and with the pump operating at a predetermined speed higher than its minimum speed the velocity of the fluid flowing in said first-mentioned second section past said branch discharge passage operates to limit the flow rate through said branch discharge passage and connected said exhaust port.

3. In a constant displacement pump operated at varying speeds, said pump comprising a casing having therein an intake chamber, a discharge chamber and intake and exhaust ports, said casing being housed Within a reservoir open to said intake port, the combination of means providing a discharge passage having a restricted portion connected to said discharge chamber, a branch discharge passage of relatively small diameter extending from said restricted portion and opening to said exhaust port, means providing a bypass passage interconnecting said discharge passage and said intake chamber, said bypass passage including a restricted portion connecting said intake port to said intake chamber, and a valve in said bypass pas- 6 sage upstream of said second-mentioned restricted portion and downstream of said first-mentioned restricted portion responsive to the pressure in said discharge passage, said valve being displaced to place said discharge passage in communication with said bypass passage when such pressure reaches la predetermined value determined by the diameter of said branch discharge passage, said pump being further characterized in operation in that flow of fluid in said bypass passage through said second-mentioned restricted portion pa-st said intake port has a supercharging action with respect to said intake chamber and in that with said valve displaced and with the pump operating at a predetermined speed higher than its minimum speed the velocity of the fluid flowing in said first-mentioned restricted portion past said branch discharge passage operates to limit the flow rate from said exhaust port.

4. In a constant displacement pump operated at varying speeds; said pump comprising pumping means located in a pumping chamber providing increasing fluid discharge with increasing speed, an intake chamber connected directly to supply fluid to said pumping chamber, a discharge chamber connected directly to receive fluid from said pumping chamber and pump inlet and outlet ports; -said pump inlet port being connected to said intake chamber; passage means connecting said discharge chamber to said intake chamber having discharge passage means connected to sa-id discharge chamber and bypass passage means connecting said discharge passage means to said -intake chamber; said discharge passage means having a discharge restriction in said passage means having less flow area than th-e remainder of said passage means to accelerate flow With increasing volume of flow; branch discharge passage means connected to said discharge passage means at said discharge restriction for providing a branch discharge pressure and a branch discharge flow in said branch discharge passage means inversely proportional to flow through :said discharge passage means to said outlet port, a valve in said bypass passage means having a valve element closing said bypass passage means in a closed position and opening said bypass passage means in an open position; said valve element being displaced by discharge pressure in said discharge passage means to open said valve; and biasing means actuated by said branch discharge pressure in said branch discharge passage means acting on said valve element to bias said valve element to the closed position proportional to said branch discharge pressure to increase the proportion `of bypass flow through said bypass passage means and decrease the proportion of outlet flow through said branch discharge passage means with increasing fluid discharge by said pumping means sufiiciently to decrease flow through said branch discharge passage means with increasing fluid discharge by said pumping means.

5. In a constant displacement pump operated at varying speeds; said pump comprising pumping means located in a pumping chamber providing increasing fluid discharge with increasing speed, an intake chamber connected directly to supply fluid to said pumping chamber, a discharge chamber connected directly to receive fluid from said pumping chamber and pump inlet and outlet ports; said pump inlet port being connected to said intake chamber; passage means connecting said discharge chamber to said intake chamber having discharge pas-sage means connected to said discharge chamber and bypass passage means connecting said discharge passage means to said intake chamber; said discharge passage means having a discharge restriction in said passage means having less flow area than the remainder of said passage means to accelerate ilow with increasing volume of flow; branch discharge passage means connected to said discharge passage means at said discharge restriction and having a branch restriction having less flow area than said discharge restriction for providing a branch discharge pressure and a branch discharge flow in said bran-ch disch-arge passage inversely proportional to flow through said discharge passage means to said outlet port, a valve in said bypass passage means having a valve element closing said bypass passage means in a closed position and opening said bypass passage means in an open position; said valve element being displaced by discharge pressure in said discharge passage means to open said valve; and biasing means actuated by said branch discharge pressure in said branch discharge passage means acting on said valve element to bias said valve element to the closed position proportional to said branch discharge pressure to increase the proportion of bypass iiow through `said bypass passage means and decrease the proportion of outlet flow through said branch discharge passage means with increasing fluid discharge by said pumping mean-s suiiiciently to decrease flow through said branch discharge passage means with increasing iiuid discharge by said pumping means.

6. In a constant displacement pump operated at varying speeds; said pump comprising pumping means located in a pumping chamber providing increasing uid discharge with increasing speed, an intake chamber connected directly to supply iiuid to said pumping chamber, a discharge chamber connected directly to receive fluid from said pumping chamber and pump inlet and outlet ports; said pump inlet port being connected to said intake chamber; passage means connecting said discharge chamber to said intake chamber having discharge passage means connected to said discharge chamber and bypass passage means connecting Isaid discharge passage means to said intake chamber; said discharge passage means having throat means providing a restriction between upstream and downstream points in said passage means to accelerate flow with increasing volume of iiow; branch discharge passage means having a restriction of less flow area than said throat means connected to said discharge passage means at said throat means and connected to said outlet port to provide a discharge pressure and a discharge ow in said branch discharge passage inversely proportional to full flow through said discharge passage means connected to said outlet port, a valve in said bypass passage means having a valve element closing said bypass passage means in a closed position and opening said bypass passage means in an open position; said valve element being displaced by uid pressure in said discharge passage means downstream of said throat to open said valve; and biasing means actuated by said discharge pressure in said branch discharge passage mean-s acting on said valve element to bias said valve element to the closed position proportional to said discharge pressure to increase the proportion of bypass flow through said valve and decrease the proportion of outlet flow through said branch discharge passage means with increasing uid discharge by said pumping means suiiiciently to decrease flow through said branch discharge passage mean-s with increasing uid discharge by said pumping means.

7. In a constant displacement pump operated at varying speeds; said pump comprising pumping means located in a pumping chamber providing increasing uid discharge with increasing speed, an intake chamber connected directly to supply uid to said pumping chamber, a discharge chamber connected directly to receive fluid from said pumping chamber and pump inlet and outlet ports; said pump inlet port being connected to said intake chamber; outlet and bypass flow control means including first passage means connecting said discharge chamber to said intake chamber having a restriction between upstream and downstream points in said irst passage means to accelerate flow and reduce pressure at the restriction, second passage means connected to said rst passage means at said restriction to connect said first passage means to said outlet port to provide outlet pressure and iiow in said second passage means inversely proportional to flow in said first passage means; and valve means having movable control means located in said rst passage means downstream of said restriction and movable between an open and closed position, pressure responsive means actuated by uid pressure in said rst passage means upstream of said movable control means to urge said movable control means toward an open position and biasing means connected to said second passage means and said movable control means operative in response to said outlet pressure to bias said movable control means toward a closed position to increase the volume of ow bypassed by said valve means and owing through said i'irst passage means and to decrease the volume of flow through said second passage means with increasing uid discharge by said pumping means sufficiently to decrease the volume of flow through said second passage means with increasing fluid discharge by said pumping means.

8. In a constant displacement pump operated at varying speeds; said pump comprising pumping means located in a pumping chamber providing increasing fluid discharge with increasing speed, an intake chamber connected directly to supply fluid to said pumping chamber, a discharge chamber connected directly to receive uid from said pumping chamber and pump inlet and outlet ports; said pump inlet port being connected to said intake chamber; outlet and bypass flow control means including first passage means connecting said discharge chamber to said intake chamber having a iirst restriction between upstream and downstream points in said iirst passage means to accelerate flow and reduce pressure at the rst restriction, second passage means having a second restriction with less ow area than said first restriction connected to said iirst passage means at said rst restriction to connect said rst passage means to said outlet port to provide outlet pressure and ow in said second passage means inversely proportional to flow in said iirst passage means; and valve means having movable control -means located in said irst passage means downstream of said restriction and movable between an open and closed position and pressure responsive means actuated by fluid pressure in said irst passage means upstream of said movable control means to urge said movable control means toward an open position and biasing means connected to said secondpassage means and said movable control means operative in response to said outlet pressure to increase the volume of ow bypassed by said valve means and owing through said first passage means and to decrease the volume of flow through said second passage means With increasing fluid discharge by said pumping means suiiiciently to decrease the volume of flow through said second passage means with increasing fluid discharge by said pumping means.

9. In a constant displacement pump operated at varying speeds; said pump comprising pumping means located in a pumping chamber providing increasing fluid discharge with increasing speed, an intake chamber connected directly to supply iiuid to said pumping chamber, a discharge chamber connected directly to receive uid from said pumping chamber and pump inlet and outlet ports; said pump inlet port being connected to said intake chamber; passage means including a bypass passage connecting said discharge chamber to said intake chamber; valve means in said passage means including a valve element closing said bypass passage in a closed position and opening said bypass passage in an open position; said valve element being displaceable by pressure in said passage means to open said valve; and flow control means including venturi means in said passage means providing a restriction restricting flow through said passage means and a variable pressure area at which static pressure decreases as fluid flow through said passage means increases while said bypass passage is |open, orifice means connecting said Variable pressure area to said pump outlet port to deliver ow to said pump outlet port at a flow rate determined by pumping chamber fluid discharge and the pressure drop across said orifice means, and biasing means controlled by fluid pressure in said pump outlet port acting on said valve element to bias said Valve element to close said valve so that said valve element is responsive to open said valve at a predetermined pumping chamber fluid discharge and pressure differential between the pressure in said passage means and the pressure in said pump outlet port to bypass fluid from said discharge chamber to said intake chamber sufficiently to decrease static pressure in said variable pressure area with continued increasing fluid flow rate through said passage means in excess of said predetermined pumping chamber fluid discharge to decrease the fluid flow rate through said orifice means to said pump outlet port with increasing pumping chamber fluid discharge.

10. In a constant displacement pump operated at varying speeds; said pump comprising pumping means located in a pumping chamber providing increasing fluid discharge with increasing speed, an intake chamber connected directly to supply fluid to said pumping chamber, a discharge chamber connected directly to receive Huid from said pumping chamber and pump inlet and outlet ports; said pump inlet port being connected to said intake chamber; passage means including a bypass passage connecting said discharge chamber to said intake chamber; valve means in said passage means including a valve element closing said bypass passage in a closed position and opening said bypass passage in an open position; -said Valve element being displaceable by pressure in said passage means to open said valve; venturi means in said passage means providing a restriction restricting flow through said passage means and a Variable pressure area at which static pressure decreases as fluid flow through said passage means increases while said bypass passage is open; orifice means connecting said variable pressure area to said pump outlet port to deliver flow to said pump outlet port at a flow rate determined by the pressure drop across said orifice means; biasing means controlled by fluid pressure in said pump outlet port acting on said valve element to bias said valve element to close said valve so that said valve element is responsive to open said valve at a predetermined pressure differential between the pressure in said passage means and the pressure in said pump outlet port; and said venturi means including said variable pressure area being proportioned relative to said orifice means so that upon said valve being opened and the flow rate to said pump outlet port reaching a predetermined flow rate range there is produced a decreasing static pressure in said variable pressure area with continued increasing fluid flow rate through said passage means during bypass flow in said bypass passage to produce a proportionally smaller fluid flow rate through said orifice means to said pump outlet port.

11. In a constant displacement pump operated at varying speeds; said pump comprising pumping means located in a pumping chamber providing increasing fluid discharge with increasing speed, an intake chamber connected directly to supply fluid to said pumping chamber, a discharge chamber connected directly to receive fluid from said pumping chamber and pump inlet and outlet ports; said pump inlet port being connected t-o said intake chamber; passage means including a bypass passage connecting said discharge chamber to said intake chamber; valve means in said passage means including a valve element closing said bypass passage in a closed position and opening said bypass passage in an open position; said valve element being displaceable by pressure in said passage means towards said open position; venturi means in said passage means providing a restriction restricting flow through said passage means and a variable pressure area at which static pressure decreases as fluid flow through said passage means increases while said bypass passage is open; orifice means connecting said Variable pressure area to said pump outlet port to deliver flow to said pump outlet port at a flow rate determined by the pressure drop across said orifice means; biasing means controlled by fluid pressure in said pump Ioutlet port acting on said Valve element to bias said valve element towards said closed position so that said valve element is responsive to fully open said valve at a predetermined pressure differential between the pressure in said passage means and the pressure in said pump outlet port; and said venturi means including said variable pressure area being proportioned relative to said ,orifice means so that when said valve is fully opened and the flow rate to said pump outlet port through said orifice means reaches a predetermined flow rate range there is produced -a decreasing static pressure in said variable pressure area with continued increasing fluid flow rate through said passage means to produce a proportionally smaller fluid flow rate through said orifice means to said pump outlet port.

References Cited by the Examiner UNITED STATES PATENTS 2,746,392 5/56 Klessig et al 103-42 2,759,423 8/56 Keel 103-42 2,977,888 4/ 61 Livermore 103-42 2,996,013 8/ 61 Thompson et al. 103-42 3,057,304 10/62 Rohde 103-136 3,059,1580 10/62 Farrell et al. 103-42 3,070,032 12/62 Rohde 103-42 3,110,266 11/ 63 Livermore 103-42 LAURENCE V. EFNER, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 207 ,077 September 2l 1965 Philip B Zeigler et al It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 39, for "predetermind" read predetermined line 45 for "statis" read static column 5 line 8, for "position" read portion Signed and sealed this 10th day of May 1966.

(SEAL) Attest:

ERNEST W. SW'IDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. IN A CONSTANT DISPLACEMENT PUMP OPERATED AT VARYING SPEEDS, SAID PUMP COMPRISING AN INTAKE CHAMBER, A DISCHARGE CHAMBER AND INTAKE AND EXHAUST PORTS, THE COMBINATION OF MEANS PROVIDING A DISCHARGE PASSAGE HAVING A RESTRICTED POSITION CONNECTED TO SAID DISCHARGE CHAMBER, A BRANCH DISCHARGE PASSAGE OF RELATIVELY SMALL DIAMETER EXTENDING FROM SAID RESTRICTED PORTION AND OPENING TO SAID EXHAUST PORT, MEANS PROVIDING A BYPASS PASSAGE INTERCONNECTING SAID DISCHARGE PASSAGE AND SAID INTAKE CHAMBER, SAID BYPASS PASSAGE INCLUDING A RESTRICTED PORTION CONNECTING SAID INTAKE PORT TO SAID INTAKE CHAMBER, AND A VALVE IN SAID BYPASS PASSAGE UPSTREAM OF SAID SECOND-MENTIONED RESTRICTED PORTION AND DOWNSTREAM OF SAID FIRST-MENTIONED RESTRICTED PORTION RESPONSIVE TO THE PRESSURE IN SAID DISCHARGE PASSAGE, SAID VALVE BEING DISPLACED TO PLACE SAID DISCHARGE PASSAGE IN COMMUNICATION WITH SAID BYPASS PASASGE WHEN SUCH PRESSURE REACHES A PREDETERMINED VALUE DETERMINED BY THE DIAMETER OF SAID BRANCH DISCHARGE PASSAGE, SAID PUMP BEING FURTHER CHARACTERIZED IN OPERATION IN THAT FLOW OF FLUID IN SAID BYPASS PASSAGE THROUGH SAID SECOND MENTIONED RESTRICTED PORTION PAST SAID INTAKE PORT HAS A SUPERCHARGING ACTION WITH RESPECT TO SAID INTAKE CHAMBER AND IN THAT WITH SAID VALVE DISPLACED AND WITH THE PUMP OPERATING AT A PREDETERMINED SPEED HIGHER THAN ITS MINIMUM SPEED THE VELOCITY OF THE FLUID FLOWING IN SAID FIRST-MENTIONED RESTRICTED PORTION PAST SAID BRANCH DISCHARGE PASSAGE OPERATES TO LIMIT THE FLOW RATE FROM SAID EXHAUST PORT. 